E200 and E220 routers have two RJ-45 interfaces, one WAN port (on the orange side) and one LAN port (on the gray side). WAN port, by default, is used as a DHCP client to connect to a primary router and get wired Internet access. If needed, this interface can be re-configured as a second LAN port, thus allowing to connect up to two Ethernet devices to a single router.
Go to Network > Load balancing > Configuration > Interfaces and delete WAN entry. Click Save afterwards.
Go to Network > Load balancing > Configuration > Members and delete WAN entry. Click Save & Apply afterwards.
Go to Network > Interfaces > WAN, set Protocol to Unmanaged and then click on Switch protocol. Click Save & Apply afterwards.
Go to Network > Firewall > Zones and make sure that Masquerading and MSS are selected for the WAN to LAN zone. Click Save afterwards.
Go to Network > Interfaces > LAN > Physical Settings and select eth0.2 (wan). Click Save & Apply afterwards.
Once these steps are performed, the router will behave as a DHCP server on its second LAN port and it should assign an IP address to any device connected via Ethernet.